Wafers are typically handled in a vacuum environment to prevent contamination of the wafers and resulting electronic chips. Since motors and the like could result in contamination of the vacuum environment and the wafers, robot arms and structure used to handle wafers are designed so that all of the motors are outside the vacuum enclosure. See, e.g., U.S. Pat. No. 6,485,250 incorporated herein by this reference.
To transport wafers and other like substrates amongst different processing modules (e.g., load ports, load locks, transport chambers, processing modules, and the like), wafer carts are used. There have also been efforts to effect magnetic levitation in driving the wafer cart in a vacuum transport chamber.
In some designs, selectively energizeable electromagnets on one or more tracks outside the vacuum chamber interact with permanent magnets on a wafer cart inside the vacuum chamber to levitate and drive the wafer cart inside the vacuum chamber. See U.S. Pat. No. 4,624,617 incorporated herein by this reference. Controlling the wafer cart so it doesn't touch the vacuum chamber walls is difficult. See published U.S. Application No. 2009/0162179, incorporated herein by this reference. More advanced designs are highly complex, expensive, may be unreliable, and utilize a significant amount of energy. See U.S. Pat. Nos. 6,183,615 and 6,684,794 incorporated herein by this reference.
In other systems, a drive unit outside the vacuum has permanent magnets and so too does the wafer shuttle inside the vacuum chamber. See U.S. Pat. Nos. 7,841,820 and 4,805,761 incorporated herein by this reference. But, permanent magnet based systems necessarily results in a wafer shuttle which must contact the vacuum chamber walls. Contamination of the vacuum chamber and thus the wafers processed therein is thus possible through friction and wear of the contact surfaces.